I am facing a strange issue while building a simple LED matrix. I am using the SK6812 LEDs and an ESP8266 controller. The LEDS will be controlled over Wifi. My matrix contains about 180 LEDs on a PCB of 25x25cm.
After about 120 flawlessly working LEDS there are strange lightning artefacts, like flickering and wrong LED color. All LEDs and the ESP are connected to the same ground. Also the logic shifter (3.3V to 5V) is working as it should. It converts the 3.3V data form the ESP to a 5V signal for the LEDs.
Additionally to the level shifting I added one 470 Ohms resistor (R2007) to the data line as suggested on this page.
Long story, short: If the 470 Ohms resistor is removed and the data line is bridged with a 0R Ohms resistor all LEDs are working flawlessly.
- I am not much of an electronics experts, and asking myself what is the purpose of this resistor? Is it safe to remove it?
- And, can this be the issue for my problem, or is it only a coincidence that removing it solved my problem?
EDIT:
The LED_DATA line is pretty long, as it travels over the whole board, front and back. My roughly length estimate would be around 13 meter. The track 0.25 mm thick and copper has a thickness of 1 Oz. Based on my calculations the resistance on the data line should be 27 Ohms.
Best Answer
As your LED_DATA trace gets longer and more LEDs get added on, the capacitance of LED_DATA will increase. It's likely that in combination with the 470ohm resistor, you're creating a lowpass filter and rounding your LED_DATA signal. As the capacitance increases and the signal gets rounder and rounder, eventually it will stop working. If that's the case, replacing it with a jumper would fix it. Try looking at the LED_DATA signal (with and without the resistor) with an oscilloscope.